Berlin 2001 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 16: Poster: Dynamics of Molecular Systems, Polymer Dynamics, Glass Transition, Crystallization, Electronic Properties of Polymers
CPP 16.17: Poster
Montag, 2. April 2001, 12:30–15:00, AT1
Crossover effects of dynamic glass transition in substances with two secondary relaxations — •H. Huth1, S. Corezzi2, K. Schröter1, M. Beiner1, and E. Donth1 — 1FB Physik, Universität Halle, 06099 Halle — 2University Perugia, INFM, I-06100 Perugia, Italy
The crossover region, where the relaxation times of α process and Johari-Goldstein β process approach each other, is characterized by pecularities of the dynamic glass transition: (i) The temperature dependence of viscosity and dielectric relaxation time τ α is changing, (ii) the cooperativity Nα(T) reaches small values of Nα ≈ 1, (iii) the extrapolated α-intensity, Δ cp(T) (or Δ єα(T)), goes for many substances to zero. Typically, the crossover temperatures examined by different methods are in good agreement.
Substances like epoxy resins DGEBA ((diglycidyl ether of bisphenol-A) and PPGE (Poly[(phenyl glycidyl ether)-co-formaldehyd]) are interesting because they have a strong γ-relaxation related to a crossover in the GHz range, and a weak β-relaxation related to a crossover in the kHz range. It is studied which pecularity can be observed in which frequency range. The results of viscosity measurements, calorimetric measurements by 3ω-method, and dielectric spectroscopy are presented. The temperature dependence of relaxation time and viscosity is analyzed. The α-intensities Δ cp(T) and Δ є α(T) as well as the cooperativity Nα(T) from fluctuation approach are extrapolated. The crossover temperatures obtained by the different methods are compared. Conclusions about the connection between secondary relaxation and cooperative dynamics are derived.